Problem: If $a + 4b = -4$ and $3x + 2y = 10$, what is $3a + 12b - 6y - 9x$ ?
$= 3a + 12b - 9x - 6y$ $= (3) \cdot (a + 4b) + (-3) \cdot (3x + 2y)$ $= (3) \cdot (-4) + (-3) \cdot (10)$ $= -12 - 30$ $= -42$